Machine and process for powder-based additive manufacturing

ABSTRACT

A machine, which is usable for additive manufacturing by sintering or melting of powder using an energy beam acting on a powder layer in a working zone, includes a device for producing a layer of the powder. The device includes a storage apparatus for storing the powder, a distributor for distributing the powder, a feeder for transferring the powder from the storage apparatus to the distributor, and a dose controller for controlling a quantity of the powder transferred from the storage apparatus to the distributor. The distributor travels over the working zone in order to distribute the powder in a layer having a final thickness adapted to the additive manufacturing. The storage apparatus is located above the working zone such that the feeder utilizes gravity. The feeder and the dose controller are movable with the distributor.

The invention relates to the machines and processes for powder-basedadditive manufacturing by sintering or melting granules of said powderusing an energy beam such as electromagnetic radiation (for example alaser beam) or a beam of particles (for example an electron beam).

More specifically, the invention relates to the means and to theprocesses for layering, that is to say for preparation, of the bed ofpowder prior to sintering or to melting of said layer using the energybeam.

Document EP-1641580-B1 in particular discloses a layering device forsintering of powders (metallic or ceramic) by laser. This devicecomprises a feed tray permitting the powder to be stored and to bedelivered in a controlled quantity to a grooved cylinder capable, on theone hand, of transferring and distributing said quantity of powder onthe depositing tray during a first passage of the cylinder on theworking zone and, on the other hand, of compacting the powder by arolling movement of the cylinder during a second passage. The powder isthen subjected to the laser beam. One disadvantage of this configurationis the size and the considerable cost of the feed tray. Anotherdisadvantage is derived from the fact that the length of the workingzone is limited by the useful perimeter of the cylinder.

Document WO-2011/007087-A2 discloses a layering device for meltingpowders by laser. This device comprises a feed tray permitting thepowder to be stored and to be delivered in a controlled quantity to ascraper system capable of feeding the depositing tray and cylinder(s)capable of distributing and compacting said quantity of powder on thedepositing tray. The powder is then subjected to the laser beam. Onedisadvantage of this configuration is the size and the considerable costof the feed tray as well as the necessary complexity of the machinebecause of the large number of tools to be controlled (scraper,distribution and/or compacting cylinder(s), rams for the trays).

Document US-2005/0263934-A1 discloses a layering device for sinteringpowders by laser. This device comprises feeding and dosing meanspermitting the powder to be delivered in a controlled quantity in thevicinity of the working zone. Feeding takes place by gravity from astock of powder situated above. A scraper permits the regulation of thethickness of a mass of powder, which is then subjected to a preheatingoperation. A rotary cylinder then permits said quantity of preheatedpowder to be transferred and distributed on the working zone. A quantityof powder may likewise be deposited on the cover of the carriagecarrying the cylinder from one side to the other of the working zone andis accordingly only applied during the return of the cylinder. Onedisadvantage of this configuration is the risk of a part (even a verysmall part) of the powder being retained on the cover and subsequentlyfalling into the working zone during the passage of the carriage abovethe bed of powder. This risk is not acceptable in the context ofindustrial use.

An additional problem that is common to the different proposals of theprior art is the difficulty and sometimes the impossibility of achievinga homogeneous thickness and density for the powder layer over the entireextent (length, width) of the working zone.

The object of the invention is thus to overcome at least one of thedisadvantages described above.

The invention proposes for this purpose a machine for additivemanufacturing by sintering or melting powder using an energy beam actingon a powder layer in a working zone, said machine comprising a devicefor producing a layer of said powder, said device comprising:

-   -   means for storing the powder,    -   means for distributing the powder able to travel over the        working zone in order to distribute the powder in a layer having        a final thickness adapted to additive manufacturing,    -   feeding means able to transfer the powder from the storage means        to the distributing means,    -   dosing means able to control the quantity of powder transferred        from the storage means to the distributing means,        said machine being characterised in that:    -   the storage means are located above the working zone,    -   the feeding means utilise gravity, and    -   the feeding means and the dosing means are able to move with the        distributing means.

Feeding by gravity via the top of the working zone and in a controlledquantity by dosing means integrated with the distributing means ensuressignificantly improved uniformity of the bed of powder than in thesystems that are familiar from the prior art.

The storage means preferably comprise a hopper, said hopper being ableto move together with the feeding means, the dosing means and thedistributing means.

The dosing means preferably comprise a rotating dosing cylinder providedwith at least one cavity, preferably a groove capable of defining a doseof powder during dosing.

The dosing means alternatively comprise a sliding trapdoor.

The distributing means preferably comprise a scraper.

The distributing means alternatively comprise a distribution cylinder,of which the height is preferably adjustable according to its angularposition.

According to a preferred embodiment of the invention, the distributingmeans and the dosing means utilise a common cylinder.

The machine according to the invention preferably in addition comprisesa compacting roller, of which the displacement in translation isintegral with the displacement of the distributing means.

The invention likewise proposes a process for additive manufacturing bysintering or melting powder using an energy beam acting on a layer ofpowder in a working zone, said machine comprising a device for layeringsaid powder, said device comprising:

-   -   means for storing the powder located above the working zone,    -   means for distributing the powder able to travel over the        working zone in order to distribute the powder in a layer having        a final thickness adapted to additive manufacturing,    -   feeding means able to transfer the powder from the storage means        to the distributing means,    -   dosing means able to control the quantity of powder transferred        from the storage means to the distributing means,        said process comprising layering stages consisting successively        of:    -   dosing a quantity of powder to be transferred from the storage        means,    -   feeding the distributing means by gravity,    -   distributing said quantity of powder on the working zone using        the distributing means,        said process being characterised in that the storage means, the        feeding means and the dosing means are integral with the        distributing means, while said distributing means travel over        the working zone.

The invention will be more readily appreciated from the rest of thedescription, which is based on the following figures:

FIG. 1 is a schematic view in cross section of a machine according tothe prior art.

FIG. 2 is a schematic view in cross section of a machine according to afirst embodiment of the invention.

FIG. 3 is a schematic view in cross section of the layering device of apreferred variant of the machine in FIG. 2.

FIG. 4 is a schematic view in cross section of the layering device of amachine according to a second embodiment of the invention.

FIG. 5 is a more detailed schematic view in cross section of a preferredvariant of the layering device in FIG. 4.

FIG. 6 is a schematic view in cross section of the layering device of amachine according to a third embodiment of the invention.

FIG. 7 is a more detailed schematic view in cross section of a preferredvariant of the layering device in FIG. 6.

FIG. 8 is a schematic view in cross section of the layering device of amachine according to a fourth embodiment of the invention.

FIGS. 9 to 12 are schematic views depicting the layering device in FIG.8 during successive stages of the layering process.

In the different figures, identical or similar elements bear the samereferences. The description of their structure and their function is notrepeated systematically, however.

In FIG. 1, a machine for additive manufacturing of a component 40according to the prior art is illustrated schematically. A source ofenergy, in this case a laser source 10, emits a laser beam 3 of whichthe orientation is controlled by mirrors that are subjected togalvanometers 20. An optical lens 30 permits the beam 3 to be focussedat the level of the working zone 4 in order to heat the upper layer ofthe powder 2 according to a precise pattern and thus to bring aboutmelting of the powder in a selective manner. After treatment of a powderlayer by the beam, the working tray 60 is lowered by a unit thicknessand is covered with a new powder layer, continuing in this manner inorder to form the component 40 layer by layer. Depending on the types ofenergy beam and the powders that are used, the thickness of a powderlayer may vary from a few micrometres (for example 10 μm) to severalhundred micrometres (for example 500 μm=0.5 mm). When the component 40is finished, that is to say when the hundreds or the thousands of layersnecessary for its construction have been successively solidified, thecomponent is removed from the working zone.

All of the parts of the machine permitting the application of a newpowder layer on the working zone are generally referred to as the“layering device”. The layering device that is familiar from the priorart comprises storage means 5 and distributing means 6 for distributingthe powder 2 on the working zone 4. As described above, the storagemeans familiar from the prior art generally make use of a verticallymobile tray 51 similar to the working tray 60. The purpose of thedistributing means 6 (not illustrated in detail in FIG. 1) is todistribute a thin layer of powder on the whole of the working zone. Thepurpose of the feeding means 7 (not illustrated in detail in FIG. 1) isto transfer the powder from the storage means to the distributing means6. The distributing means and the feeding means that are familiar fromthe prior art commonly make use of scrapers and/or rollers carried byone or a plurality of carriages, said carriages being mobile between thestorage means 5 and the working zone 4. Dosing means 8, in this casemeans permitting the raising of the mobile tray 51 to be controlledprecisely, permit the quantity of powder used for each operation of thelayering device to be controlled. Once the distributing means have movedacross the working zone (towards the left in FIG. 1), the surplus powderis pushed into a recovery container 21.

FIG. 2 represents a first embodiment of the machine 1 according to theinvention and, in particular, an embodiment of its layering device. Thesource and the control of the energy beam are illustrated in a mannerthat is identical to the prior art. This is only one example. Asdescribed in the preamble to the application, the invention isapplicable in reality to all the types of powder-based additivemanufacturing by sintering or by total melting of the granules of saidpowder using an energy beam such as electromagnetic radiation (forexample a laser beam) or a beam of particles (for example an electronbeam). The rest of the present description thus concentrates principallyon the process and the layering device.

The storage means 5 have the form of a hopper 52 located above the planeof the working zone 4. The distributing means 6 use a scraper 61. Thescraper is integral with the hopper. The feeding means 7 simply use alower opening 71 in the hopper in order to transfer the powder towardsthe distributing means 6 by gravity. Dosing means, in the form of arotating dosing cylinder 81 comprising at least one cavity, permit thequantity of powder transferred to be controlled. Said cavity, preferablya groove 82, defines a reproducible dose of powder. The one or moregrooves 82 extend substantially for the whole of the useful length ofthe dosing cylinder 81, that is to say substantially for the whole ofthe width of the working zone 4. The dimensions and the form of thecross section of the grooves 82 may vary along the length of thecylinder 81 in order to further improve the distribution of the powderon the whole of the working zone.

In FIG. 3, the device in FIG. 2 is depicted during the layeringoperation. The thicknesses of powder are generally shown highlymagnified in the present application in order for them to be readilyvisible by the reader, as is often also the case in the documentsassociated with the prior art. It is, in point of fact, impossible toshow a thickness of 50 μm and a working zone of 500 mm in length, forexample, in the same drawing while faithfully respecting theproportions.

In FIG. 3, the hopper 52 is displaced towards the left of the figure atthe same time as the scraper 61. The scraper distributes and smoothesthe powder layer on the working zone 4. The mass 22 of powder situatedahead of the scraper is dosed by the dosing cylinder 81. The applicationof powder may take place on a single occasion for each layer. The dosageis preferably progressive, however, that is to say that the applicationof powder takes place progressively by delivering the contents of agroove on a number of occasions in the course of the passage over theworking zone, which permits the variability of the working conditions ofthe scraper to be reduced and, accordingly, an improved regularity ofthe thickness and the compactness of the resulting bed of powder to beguaranteed.

FIG. 3 illustrates in addition a preferred variant of the firstembodiment of the invention, in which a compacting roller 9 is used inaddition. The final thickness 24 of the layer 23 of powder is thus theresult of two successive operations. A first thickness is defined by thedistributing means 6, in this case the scraper 61. This thickness isthen reduced and is made even more homogeneous by the action of thecompacting roller 9. The roller is displaced together with the hopperand the scraper. More preferably, the roller is counter-rotating, thatis to say that it is motorized in such a way as to rotate in theopposite direction to its displacement relative to the bed of powder (asindicated by the arrow, which shows a rotation in the clockwisedirection, while the roller is moving towards the left).

Depicted in FIG. 4 is a second embodiment of the layering device, inwhich the distributing means 6 use a distribution cylinder 62 in placeof the scraper of the first embodiment. The displacement of thedistribution cylinder 62 is linked to that of the hopper 51, as in thecase of the scraper 61 in the first embodiment. The cylinder 62 may befixed in rotation or counter-rotating. When the distribution cylinder isfixed, its fixation 63 is preferably eccentric, which permits the fineregulation of its height and thus of the final thickness 24 of theresulting powder layer 23.

As depicted in FIG. 5, a counter-rotating compacting roller 9 may beadvantageously associated with the layering device according to thesecond embodiment under the same conditions as those described abovewith reference to FIG. 3.

FIG. 6 depicts a third embodiment. It differs in principle from thefirst embodiment in that the dosing means 8 use a sliding trapdoor 84,of which the duration and the amplitude of opening influence thequantity of powder transferred to the distributing means 6. Preferably,the storage means 5 use a flexible hopper 53 carried by a hopper support54 in order to reduce the risk of blocking of the powder. Depending onthe types of powder used, supplementary active unblocking means (notillustrated here) may be deployed.

Depicted in FIG. 7 is a variant of the third embodiment comprising inaddition a counter-rotating compacting roller 9, of which thedisplacements are integral with the scraper and the hopper, as describedabove with reference to FIG. 3.

FIG. 8 depicts a fourth embodiment of the layering device according tothe invention, in which the dosing means 8 and the distributing means 6use a common rotating cylinder 64. The dosage function is assured by agroove 82 in the common cylinder 64 according to the principle describedabove with reference to FIG. 2. The distribution function is assured bya smoothing section 65 of the common cylinder 64 according to theprinciple described above with reference to FIG. 4. One advantage ofthis embodiment is that it permits further lightening of the layeringdevice of the machine according to the invention. The common cylinder 64is preferably fixed in rotation during its displacement on the workingzone. The smoothing section 65, that is to say the part of the commoncylinder that is intended for the distribution of the powder, isdelimited symbolically by dotted lines in FIGS. 8 to 12. This sectionpreferably includes a swelling 66. This swelling of low overall height(for example a few tenths of a millimetre at most) is scarcelyperceptible in the figures in spite of its magnification.

The operation of this embodiment is illustrated in detail in FIGS. 9 to12, which show the successive configurations of the device in the courseof a layering cycle.

In FIG. 9, the layering device is in a waiting configuration, forexample between two successive layers. The powder 2 is retained in theclosed hopper 52 by the hermetic contact of the common cylinder 64. Thegroove 82 is then able to charge itself with powder.

In FIG. 10, the common cylinder 64 has rotated through about half arevolution in the anticlockwise direction and has deposited a dose ofpowder in the vicinity of the working zone 4.

In FIG. 11, the common cylinder 64 has rotated through about a quarterof a revolution in the clockwise direction in order to bring thesmoothing section 65 into contact with the mass of powder 22 and at theappropriate height. The fact that the smoothing section includes aswelling 66 permits the fine regulation of the smoothing thickness bythe choice of the angle adopted by the common cylinder 64.

In FIG. 12, the layering device passes over the working zone 4, asdescribed previously, pushing the mass of powder 22 above the component40 in order to smooth a powder layer 23 having a final thickness 24. Inorder to limit the variations in pressure over the entire length of theworking zone, the feed phase described in FIGS. 9 and 10 may be repeatedon one or a number of occasions in the course of a single passage overthe working zone, in which case the dose defined by the groove 82preferably represents a fraction of the quantity of powder necessary fora complete layer.

Alternatively, the powder depositing phase may be performed severaltimes in succession in the absence of any smoothing movement in order tocreate, in the configuration in FIG. 10, a mass 22 corresponding to aplurality of unit doses as defined by the groove 82.

It should be noted (as explained above) that the thicknesses of thelayers, the volumes of the masses, the grooves or the swelling 66 arenot represented on a consistent scale and, quite the reverse, aredeliberately distorted for the purpose of making the figures legible.

Of course, as described above for the other embodiments of the invention(see, for example, the embodiment in FIG. 7), the layering device inFIGS. 8 to 12 may preferably comprise in addition a counter-rotatingcompactor roller (not illustrated here), of which the displacement isintegral with the displacement of the feeding means and the dosingmeans, that is to say in this case with the hopper 52 and the commoncylinder 64.

Alternatively, the smoothing section 65 of the common cylinder 64 mayexhibit a reduction in radius at the point of the increase in the radius(swelling 66) illustrated and described with reference to FIGS. 9 to 12.Whether this involves an increase or a reduction in the radius, it isthis variation in the radius that permits the adjustment of the heightof the cylinder (and thus the fine adjustment of the smoothingthickness) by the choice of the angle adopted by the common cylinder 64.

It will be appreciated that a layer may be produced according to theinvention in a single pass, that is to say in a single passage over theworking zone. The quantity of powder stored in the hopper is preferablysufficient to produce hundreds, and even thousands, of layers, that isto say that the machine could achieve additive manufacturing of a singlecomplete component, or even of a plurality of complete components,without recharging the hopper. Recharging of the hopper preferably takesplace at the moment when the manufacturing of a component is completed,and the finished component is preferably removed before newmanufacturing commences.

The powder used is preferably a metallic or ceramic powder. Depending onthe types of energy beams that are used and depending on the thicknessof the final layer referred to here, the average diameter of theparticles of the powder may vary from a few microns (for example 5 μm)to 300 or 400 μm.

A person skilled in the art will appreciate that the differentembodiments described and illustrated here are specific examples ofcombinations of means according to the invention. Other obviouscombinations or substitutions of the different means are likewise partof the invention, for example the replacement in the third embodiment(FIGS. 6 and 7) of the scraper 61 by a distribution cylinder 62according to the second embodiment in FIGS. 4 and 5.

1-10. (canceled) 11: A machine for additive manufacturing by sinteringor melting powder using an energy beam acting on a powder layer in aworking zone, the machine comprising a device for producing a layer ofthe powder, wherein the device includes: a storage apparatus, whichstores the powder, a distributor, which distributes the powder in alayer having a final thickness adapted to the additive manufacturing,the distributor being movable to travel over the working zone, a feeder,which transfers the powder from the storage apparatus to thedistributor, and a dose controller, which controls a quantity of thepowder transferred from the storage apparatus to the distributor,wherein the storage apparatus is located above the working zone, whereinthe feeder utilizes gravity, and wherein the feeder and the dosecontroller are movable with the distributor. 12: The machine accordingto claim 11, wherein the storage apparatus includes a hopper, which ismovable with the feeder, the dose controller, and the distributor. 13:The machine according to claim 11, wherein the dose controller includesa rotating dosing cylinder provided with at least one cavity, eachcavity defining a dose of the powder during a dosing operation. 14: Themachine according to claim 13, wherein the at least one cavity is or areformed of at least one groove, each groove defining the dose of thepowder during the dosing operation. 15: The machine according to claim11, wherein the dose controller includes a sliding trapdoor. 16: Themachine according to claim 11, wherein the distributor includes ascraper. 17: The machine according to claim 11, wherein the distributorincludes a distribution cylinder. 18: The machine according to claim 17,wherein a height of the distribution cylinder is adjustable according toan angular position of the distribution cylinder. 19: The machineaccording to claim 11, wherein the distributor and the dose controllerutilize a common cylinder. 20: The machine according to claim 13,wherein the distributor and the dose controller utilize a commoncylinder. 21: The machine according to claim 17, wherein the distributorand the dose controller utilize a common cylinder. 22: The machineaccording to claim 11, wherein the device further includes a compactingroller, and wherein a displacement in translation of the compactingroller is integral with a displacement of the distributor. 23: A processfor additive manufacturing by sintering or melting powder using anenergy beam acting on a powder layer in a working zone, the processcomprising steps of: dosing, using a dose controller, a quantity of thepowder to be transferred from a storage apparatus to a feeder; feeding,using the feeder, the quantity of the powder from the storage apparatusto a distributor by gravity; and distributing, using the distributor,the quantity of the powder on the working zone, wherein the storageapparatus, the feeder, and the dose controller move integrally with thedistributor while the distributor travels over the working zone, andwherein the dosing step, the feeding step, and the distributing step arerepeated successively in a plurality of layering stages.